Herbicidal sulfamoyl urea compounds are described in U.S. Pat. Nos. 4,622,065, 5,009,699 and 5,280,007, among others. The crop-selective sulfamoyl urea herbicidal agent 1-{[o-(cyclopropylcarbonyl)-phenyl]sulfamoyl}-3-(4,6-dimethoxy-2-pyrimidin yl)urea is described in U.S. Pat. No. 5,009,699. This sulfamoyl urea compound demonstrates a superior margin of safety toward crop plants, especially rice plants, while concomitantly controlling broadleaf weeds and sedges.
4-Halo-2'-nitrobutyrophenone compounds are key intermediates in the preparation of sulfamoyl urea herbicides. 4-Halo-2'-nitrobutyrophenone compounds and their multi-step preparations from the magnesium enolate of acetylbutyrolactone are described in U.S. Pat. No. 4,075,346 and copending U.S. patent application Ser. No. 08/161,382 filed on Dec. 2, 1993. However, these methods require multiple chemical reactions which increase chemical waste and reduce cost-effectiveness.
It is an object of the present invention to provide an efficient single-step method for the preparation of 4-halo-2'-nitrobutyrophenone compounds which eliminates the use of hydrogen halide reactants, reduces waste and increases cost-efficiency.